Adaptive digital baseband predistortion

Abstract

Introduction The radio frequency (RF) power amplifier (PA) is the most power consuming element in a wireless transmission system, and can account for more than 50 percent of the total power consumed by the transmitter [1]. Improving the PA efficiency saves energy and drives down the overall system costs. A study described in [2, p. 13] provides a compelling reason for PA linearization: application of PA linearization technologies can yield annual savings of millions of dollars for a typical network service provider. Efficient PAs are usually nonlinear. Nonlinearity generates both in-band distortion and out-of-band interference, which manifest in terms of transmitter error vector magnitude (EVM) degradation and spectral regrowth. In wireless communication systems, many signal formats, such as Code Division Multiple Access (CDMA) and Orthogonal Frequency Division Multiplexing (OFDM) transmission, have been introduced to improve spectrum efficiency and data rate. However, these non-constant-envelope signals are not power efficient in the presence of nonlinear PAs as large back-offs are needed for linear transmission. In most commercial wireless communication systems, PAs are still the dominant source of signal quality degradation since the PAs are usually biased in a mildly nonlinear region to gain a reasonable amount of efficiency.